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First Steps

StarDate:

December 5, 2012

To understand a star, you need to know how far away it. Its distance reveals how big and bright it is, for example, which helps reveal what’s happening inside the star.

But measuring astronomical distances is tough. You can’t drive out to a star and measure the miles as they click by. Instead, astronomers have developed a “stepladder” approach. Each rung on the ladder helps measure distances to farther objects.

Texas astronomer Fritz Benedict and his colleagues have helped solidify one of the first steps on that ladder. Using Hubble Space Telescope, they’ve measured the distances to several stars that pulse like beating hearts.

RR Lyrae stars get bigger and smaller over a period of half a day or so. There’s a relationship between the length of each “beat” and the star’s true brightness. That means you can compute the star’s distance by comparing the length of its pulses to how bright the star appears in the sky.

For the technique to work, though, astronomers first must use another technique, called parallax, to find the distances to a few RR Lyrae stars. Benedict’s team did that for five stars, using Hubble to measure the position of each star when Earth was on opposite sides of the Sun, providing a slightly different viewing angle.

Before this project, astronomers had a good measurement for only one RR Lyrae star — the prototype, RR Lyrae itself. The measurements of more stars help make that rung on the distance ladder a good bit sturdier.

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